Dr. Ravi Samtaney has an extensive background in computational mathematics and physics with emphasis on large-scale high-performance computing, advanced numerical methods and innovative algorithms which he has applied to solve a variety of problems in areas of nonlinear physics, turbulence, fluid and magnetohydro dynamics, computer graphics and computational endocrinology. He is making a committed transition to medicine and biology, where he will apply his knowledge of advanced computing techniques to cardiac electrophysiology. He will be joining the Division of Cardiology at UCLA, where he will be mentored by Professors Alan Garfinkel and James N. Weiss. Dr. Samtaney's immediate career goal is to be trained both formally by taking courses for credit in physiology and medicine; and by conducting research in cardiology simulations under his mentors. His long-term career goal is to start an independent research program in computational biology with extensive ties to biomedical engineering and medicine. His research career development plan consists of: formal course work at UCLA in physiology and medicine; attending research seminars, research group meetings; and attending and presenting research papers at conferences. The specific aims of the proposed research are to: (1) Apply adaptive mesh refinement algorithms to provide a "numerical microscope" to provide high resolution in areas such as wave fronts of the wave of excitation in cardiac tissue and to resolve small-scale tissue hetereogeneity, especially dispersion of refractoriness, a principal cause of wavebreak and re-entrant arrhythmia; (2) Apply a level-set based method to perform simulations in realistic cardiac anatomy. The aim is address the role of cardiac anatomic structure as a predisposing factor to fibrillation. Further the level-set method is an excellent tool to simulate cardiac tissue in motion, and to take into account the biodomain structure of heart tissue; and (3) model the genesis of arrythmias and comparison of model predictions with experiments. These simulations will examine the factors causing spiral wave breakup, the chief mechanism of ventricular fibrillation, which is the leading cause of sudden cardiac death.